The present invention is generally directed to a method and apparatus for three dimensional display of connected substructures within a body. More particularly, the present invention is directed to a system and method for the display of medical and other images produced from magnetic resonance imaging devices and from computerized axial tomographic machines. Even more particularly, the present invention is directed to a display system in which connected anatomical features are isolated for three dimensional display.
Computerized axial tomography and related x-ray imaging systems are capable of producing signal patterns representing the value of at least one physical property associated with substructures within a three dimensional body. In the case of medical imaging, the body typically comprises a patient or patient limb. In the case of industrial systems, the body may comprise a turbine blade or other part exhibiting an internal structure. Additionally, magnetic resonance imaging systems are also particularly capable of generating such data for various biological life forms. In the case of x-ray tomography, the physical property being measured is typically an x-ray absorption coefficient associated with various locations throughout a body. In the case of magnetic resonance imaging, nuclear precession decay signals are typically measured. However, the present invention is not confined to utilization with either computerized axial tomography systems or with magnetic resonance imaging systems. For example, positron emission tomography and single photon emission radiography systems may also be employed in conjunction with the system and method of the present invention. For the purposes of the present invention, the most relevant feature of such systems is their ability to generate signal patterns representing the value of one or more physical properties associated with various substructures within the body at regularly spaced cell or grid locations.
In three U.S. Patents assigned to the same assignee as the present invention, systems and methods for the display of three dimensional data are disclosed. These are: U.S. Pat. No. 4,729,098 filed June 6, 1985 titled "System and Method Employing Nonlinear Interpolation for the Display of Surface Structures Contained Within the Interior Region of a Solid Body" and U.S. Pat. No. 4,710,876 filed June 6, 1985 titled "System and Method for the Display of Surface Structures Within the Interior Region of a Solid Body" and U.S. Pat. No. 4,719,585 filed Aug. 28, 1985 titled "Dividing Cube System and Method for the Display of Surface Structures Contained Within the Interior Region of a Solid Body". All three of these patents are hereby incorporated herein by reference. These patents generally describe the marching cubes and dividing cubes systems for the display of shaded images on a display device such as a cathode ray tube (CRT). The present system and method can be thought of as a preprocessor for the production of data to be supplied to dividing cubes or marching cubes systems. These systems typically employ information supplied from magnetic resonance imaging or CAT scanner x-ray systems (although they are not limited thereto). They produce a shaded image on a screen in such a manner as to create, with shading, the illusion of a true three dimensional view on a two dimensional screen. By the operator choosing certain data value ranges, it is possible for such systems to display only bone tissue, or only other soft tissue structures. These systems also readily permit the sectioning of the data so as to produce a shaded three dimensional image which accurately depicts those structures which would be visible if the body were sliced in a specified direction. Such systems provide radiologists and surgeons with extensive preoperative information to enable them to more precisely and accurately carry out the intended surgical procedure. It should be particularly noted with respect to systems of the present invention that, in general, all views are provided from a single set of data collected at one time from the patient. The data is typically collected as a sequence of tomographic slice data. However, it is also possible to collect data over various periods of time, when necessary for the purpose of monitoring temporal changes within the patient's body.
While the three dimensional display systems described in the above-identified patents operate to quickly and effectively display highly desirable medical information, there is nonetheless other information which is contained within the data which is not readily viewable by the above-described systems. In particular, while the systems described in the patent applications described above are capable of selectively displaying only those tissues which exhibit data values in a specified range, there may be several different organs or tissues which also exhibit physical property data values in the same range. All such structures are either entirely displayed or entirely eliminated from view in the systems described in these patent applications. For example, it would be desirable to be able to isolate a particular bone from data which relates to several different, non-connected bone structures. Likewise, it would also be desirable to display images of a vascular network isolated from surrounding tissue. Similarly, it would be desirable to display images of the brain isolated from other similar head tissues such as skin. While it is relatively easy to isolate brain tissue from surrounding bone tissue because of their different physical properties, the similarity of brain and facial tissue properties makes isolation for viewing more difficult. However, advantage is taken in the system and method of the present invention of the fact that brain and facial skin tissue, for example, are not physically connected tissue structures. Accordingly, the present invention employs geometric connectivity of adjacent structures to isolate, for display purposes, select substructures within a solid body being imaged. The system and method described herein are seen to be particularly well adapted for use in conjunction with either the marching cubes or dividing cubes systems described above.